Mamiya RB67 Sekor C 50mm F4.5 wide angle lens for use with Mamiya Pro-S

The Mamiya  RB lens system mount which is a bayonet type system with a locking ring. Lenses are equipped with Seiko leaf shutters and focus is set on the camera body using a bellows arrangement with a 46mm extension. The click stops can be at half-stop aperture settings, but the shutter speeds can only be set at full stops. A depth of field preview lever is also built-in to the lens. The lenses typically have shutter speeds of 1 to 1/400 of a sec. and a T mode. The T mode, keeps the lens shutter open until the shutter ring is moved onto the 1 sec mark or when the shutter cocking lever is pressed slightly. Since it’s a leaf shutter based camera, electronic flash sync is available at all speeds. Since the system is synchronized, the camera body and lens must be cocked before attaching or removing the lens. To cock the lens ensure that the pins are in-line with the red indicators. A majority of the lenses use a screw on 77mm filter making it much easier to swap filters between lenses.

Mamiya -Sekor C 50mm F4.5 lens

• Angle of View: 82 ˚
• Construction: 11 elements 8 groups
• Filter Size: 77mm
• Minimum Focus: .13 ft
• Weight: 780g
• Floating Element:  This lens has a floating element which is moved by a seperate ring marked with green numbers, located in the front of the shutter speed ring. Most lenses, like this one, are designed to have the best sharpness when focused at infinity. Other lenses, like many macro lenses, are designed to have the best sharpness when focused closely. The floating element allows you to get the best sharpness at a range of focusing distances.

• Notes: Acceptable results can be had by setting the floating element ring at infinity. This will give acceptable focus from about 7 feet to infinity. Setting the ring at 3.3 feet gives acceptable result from 3.3  to about 7 feet. If focusing closer, set at 3.3 feet at stop down as much as possible.
• Using: To use the lens, first focus with the bellows focusing. Second, use the focusing scale on the side of the body or a tape measure to find the focusing distance. Third, align the floating element ring so that the green number matching the distance lines up with the red dot on the depth of field scale